This invention is generally directed to processes for the preparation of chalcogenide alloys, and more specifically the present invention is directed to the preparation of chalcogenide alloys in high purity by simultaneously oxidizing a solution of alkaline selenium and alkaline tellurium compounds. Accordingly, there is provided in accordance with the present invention a simple, high yield, economically attractive, low temperature process for the direct preparation of chalcogenide alloys of high purity. The resulting chalcogenide alloys are useful, for example, in the preparation of imaging members, particularly xerographic photoconductive members that can be incorporated into electrophotographicimaging processes.
The incorporation of selenium or selenium alloys into xerographic imaging members is well known. These members can be subjected to a uniform electrostatic charge for the purpose of sensitizing the surface of the photoconductive layer, followed by exposure of an image to activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating member, and wherein a latent electrostatic image is formed in the nonilluminated areas. The resulting image may then be developed and rendered visible by depositing thereon a toner composition containing resin particles and pigment particles.
Many processes are known for the preparation of chalcogenide alloys, particularly selenium containing alloys including, for example, melt blending of the elemental substances such as selenium and arsenic in the proportions desired in the final alloy product. Thus, for example, there is disclosed in U.S. Patent 3,634,134 the preparation of arsenic-selenium alloys by blending. This method not only involves high temperatures, but in most instances, crystalline materials are not obtained. Further, in many instances depending on the process parameters, the desired allloy is not obtained; rather by following, for example, the melt blending process, there is obtained an unhomogeneous mixture of arsenic, selenium, and an arsenic selenium alloy. Additionally, in these processes, there must be selected for evaporation high purity arsenic and high purity selenium, that is 99.999 percent pure; and moreover processes for obtaining high purity arsenic and selenium precursors usually require high temperature distillations which are not desirable. A similar melt blending method for preparing selenium alloys is disclosed in U.S. Pat. No. 3,911,091.
Also, there is disclosed in U.S. Pat. No. 4,007,255 a process for preparing stable red amorphous selenium containing thallium by precipitating selenious acid with from about 10 parts per million to about 10,000 parts per million of thallium dioxide with hydrazine from a solution thereof, and methanol or ethanol containing not more than about 50 percent by weight of water at a temperature between about -20.degree. C. and the freezing point of the solution wherein the resulting precipitate is maintained at a temperature of from about a -13.degree. C. to about a -3.degree. C. A similar teaching is present in U.S. Pat. No. 4,009,249 wherein stable red selenium is formulated.
Disclosed in U.S. Pat. No. 3,723,105 is a process for preparing a selenium-tellurium alloy by heating a mixture of selenium and tellurium containing 1 to 25 percent by weight of tellurium to a temperature not lower than 350.degree. C. to melt the mixture, followed by cooling gradually the molten selenium and tellurium to around the melting point of the selenium tellurium alloy at a rate not higher than 100.degree. C. per hour, and subsequently quenching to room temperature within 10 minutes.
Further, there is disclosed in U.S. Pat. No. 4,121,981 the preparation of a selenium alloy by, for example, electrochemically codepositing selenium and tellurium onto a substrate from a solution of their ions wherein the relative amount of alloy deposited on the cathode is controlled by the concentrations of the selenium and the tellurium in the electrolyte, and by other electrochemical conditions. Once the selenium tellurium layer deposited on the cathode has reached the desired thickness, deposition is discontinued and the cathode is removed.
Additionally, there is disclosed in U.S. Pat. No. 3,524,745 the preparation of an arsenic antimony selenium alloy by heating a mixture of these materials at a temperature of 600.degree. C. for a period of several hours in a vacuum, followed by air cooling to room temperature. According to the teachings of this patent, the cooled alloy, depending on the initial composition, is completely polycrystalline, a mixture of crystalline and amorphous phases, or completely amorphous.
Furthermore, there is disclosed in U.S. Pat. No. 4,460,408, the disclosure of which is totally incorporated herein by reference, a process for the preparation of chalcogenide alloys of high purity by the simultaneous coreduction of the corresponding esters subsequent to isolation and purification. More specifically, there is disclosed in this patent a process for the preparation of chalcogenide alloys in high purity comprising providing pure esters of the desired chalcogens, and subsequently subjecting the mixture of pure esters to a coreduction reaction with, for example, hydrazine. Also of interest is the prior art referred to in this patent, reference for example columns 1 and 2 thereof. In the process of the present invention, isolated pure esters are not involved, rather a solution of the oxides are subjected to a cooxidation reaction.
In addition, there is illustrated in U.S. Pat. No. 4,484,945, the disclosure of which is totally incorporated herein by reference, the preparation of chalcogenide alloys in high purity, which comprises providing a solution mixture of oxides of the desired chalcogens, and subsequently subjecting this mixture to a simultaneous coreduction reaction.
Other patents of interest include 3,577,216, which discloses a process for the recovery of selenium (IV) wherein the metallic selenide is precipitated from a reaction medium subsequent to the utilization of the aforementioned selenium as a catalyst in the oxidation of organic compounds by an oxidizing agent; 4,576,634, which illustrates the process for the preparation of selenium tellurium alloys by a reduction of an acid mixture of selenium and tellurium solutions; and 4,484,945, which discloses the preparation of selenium alloys by the coreduction of the corresponding chalcogenide esters oxides.
Although the process as mentioned herein as well as others are suitable for their intended purposes, with the primary exception of the processes disclosed in the Xerox patents mentioned such as U.S. Pat. Nos. 4,576,634; 4,460,408; and 4,484,945, these processes require high temperatures and distillations. Further, in some instances the aforementioned processes result in selenium alloys which have differing electrical properties which is believed to be the result of inhomogeneities known to exist in nonequilibrium glasses. In addition, the prior art processes for preparing alloys with the exception of the processes disclosed in many of the Xerox patents mentioned are not economical. Therefore, there is a need for new processes for preparing chalcogenide alloys that are economically attractive, and wherein there results alloys of high purity. Also, there is a need for improved processes wherein chalcogenide alloys can be obtained in high purity by utilizing substantially similar process parameters and apparatuses. Further, there continues to be a need for improved processes for the preparation of high purity chalcogenide alloys wherein some of the reactants selected can be recycled. Moreover, there continues to be a need for improved processes for preparing chalcogenide alloys that are homogeneous, are of a crystalline form, and can be obtained in various proportions without using high temperature reaction conditions, and without isolating and purifying any resulting intermediates. There is also a need for processes wherein chalcogenide alloys such as selenium and tellurium intermediates are cooxidized from a-2 valency to a 0 valency. There are also a need for a simple improved process for the direct preparation of selenium tellurium alloys wherein a solution co-oxidation can be accomplished in an effective manner. There are also a need for processes for the preparation of chalcogenide alloys, particularly selenium tellurium alloys wherein substantially no environmental hazards are associated therewith. These and other needs can be satisfied in accordance with the process of the present invention wherein substantially homogeneous chalcogenide crystalline alloys are obtained by the solution oxidation of a mixture of alkaline selenium and alkaline tellurium compounds.